A number of different physical treatments of starch have been proposed in the past, but, to our knowledge, physical modification by the methods used on starch have not been proposed for physical modification of starchy flours. One of the earliest physical treatments used on starch is dextrinization by heat, generally believed to have had its origins from observing the effect of the intense heat of a fire on starch stored in a warehouse ("British Gums"). "Brewer's grits" can be made from starch by a combination of heat and pressure applied to a thick starch slurry, usually by means of a drum dryer. The starch becomes gelatinized, and forms a film on the rotating dryer drum. The starch film is dried and then broken into small chunks to make a dustless grit product. Such "grits" are convenient to use in breweries as a carbohydrate source for fermentation.
One difficulty with heat treating a starchy flour in an aqueous slurry is that the starch component gelatinizes, and loses its discrete granular form. The gelatinized starch cannot be filtered, and excess water is difficult to remove without further changing the properties of the starchy flour. It is therefore desirable to preserve the granular structure of the starch component to the extent possible by using other liquids, such as lower alcohol, in which the starch component of the flour retains its granular structure, or at least some semblance of a granule form which is filterable, thereby making it possible to separate the physically modified starchy flour from the process liquid.
Various patents describe treating starch in alcohol, but none were found which describe such treatment of a starchy flour. Typical of such patents showing starch treatment is U.S. Pat. No. 2,587,650 issued Mar. 4, 1952 to Carl E. Rist et al. This patent describes the use of a lower alkanol (methanol, 85 volume percent), heat (105.degree.-125.degree. C.), and pressure (1 and 6 atmospheres or more) to physically treat starch. This reference points out that the process is "readily adaptable to continuous operation and/or to recycling and reuse of the extracting solvent" (Column 3, lines 45-46). There is no mention of similarly treating starchy flours, however.
A somewhat later series of patents includes U.S. Pat. No. 3,586,536 issued June 22, 1971. This patent describes heating starch slurried in methanol in a confined zone to a temperature in the range of 225.degree. F. to about 300.degree. F. for a time "not in excess of thirty minutes." There is no description of such treatment of starchy flours, though. This patent states that "ethanol, isopropanol and acetone are considered to be inoperable in our invention." See: U.S. Pat. No. 3,586,536, Column 7, lines 2-4. These latter organic liquids were said to result in either insufficient reduction of the fat content of the starch, or incipient gelatinization of the starch.
U.S. Pat. No. 3,617,383 issued Nov. 2, 1971 to Thurston et al., describes in great detail the effect on starch caused by the solvent treatment of starch in a confined zone. The process temperatures in the examples range from 230.degree.-320.degree. F. Starchy flours are not disclosed as a substance which may be subjected to the method described in this patent, however.